The present invention relates generally to the field of magnetic recording heads. In particular, the present invention relates to a magnetic recording head having controlled remnant magnetization.
In an electronic data storage and retrieval system, a transducing head typically includes a writer for storing magnetically-encoded information on a magnetic disc and a reader for retrieving that magnetically-encoded information from the magnetic disc. The reader typically includes two shields and a magnetoresistive (MR) sensor positioned between the shields. Magnetic field from the surface of the disc causes oscillation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
When the magnetic disc stores data based on magnetization directions generally perpendicular to the plane of the disc, the writer typically includes a write pole and a return pole, but can operate with no return pole. The poles are separated from each other at an air bearing surface of the writer by a gap layer and are connected to each other at a region distal from the air bearing surface by a back gap closer or back via. An alternative writer design uses two return poles, one positioned on each side of the write pole. The air bearing surface is the surface of the recording head that faces the magnetic medium or disc. One or more layers of conductive coils are positioned between the write and return poles, and are encapsulated by insulating layers. The writer and the reader may be arranged in a merged configuration in which a shared pole serves as both the top shield of the reader and the return pole of the writer.
To write data to the perpendicular recording magnetic medium, an electric current is caused to flow through the conductive coils to induce a magnetic field across the write gap between the write pole and the return pole. By reversing the direction of the current through the coils, the polarity of the data written to the magnetic media is reversed. Because the write pole is generally the trailing pole of the write and return poles, the write pole is used to physically write the data to the magnetic medium. Accordingly, it is the write pole that defines the track width of the written data. More specifically, the track width is defined by the width of the write pole at the air bearing surface.
It is desirable that the write pole and the return pole are fabricated such that their magnetization directions are parallel to the ABS when no writing is taking place. Thus, there should be no net magnetic field in the direction perpendicular to the ABS after the write process is completed. However, this is not always the case. Any non-uniformity or defects in the film structure can result in net magnetization in a direction perpendicular to the ABS or non-uniform magnetization. Other causes of non-uniform magnetization include improper film shape, stresses, film structure non-uniformities, or inherited extrinsic hysteresis properties.
Moreover, stray magnetic fields also exist in the disc drive environment. Although the write head may be idle, the presence of stray magnetic fields created by external sources can cause net magnetization of the write pole in a direction perpendicular to the ABS.
The net magnetization at the write pole in a direction perpendicular to the ABS when no writing is taking place can result in unintended destruction of data that has already been written. This is particularly problematic when a double-layer perpendicular recording medium has a highly permeable NiFe soft magnetic underlayer, which magnifies these fringing fields.
Thus, there is a need in the art for a write head that prevents unwanted writing by the write pole when the write pole is supposed to be idle.